The development of successful gene therapy approaches to lymphoma and other tumors will require the construction of vectors that specifically home to the cancerous tissues, and appropriate models in which to evaluate these vectors. We propose a novel approach to redirect a virus to target lymphoma using CD40 and CD40 ligand. This approach will be tested in spontaneous canine lymphoma, a rigorous model of the human disease. We will use a recombinant adenovirus system, in which trimerization of the fiber occurs through the fibritin trimerization domain and targeting is provided by canine CD40 ligand which will target these vectors to CD40 positive canine cells. Both Ad5 and Canine Adenovirus, type 2 (CAV-2) vectors will be developed. The use of canine adenovirus creates a 'syngeneic'model in which the interactions of host and viral systems can be studied and allows comparison to the Ad5 vector. Vectors specifically targeted to canine B-cell lymphoma using CD40 ligand will be assessed for delivery potential in dendritic cells and cultured primary canine tumor cells. Subsequently, the virus will be labeled with a Technetium marker and injected into dogs with lymphoma, allowing the localization of the vector to tumor to be visualized. Finally, the ability of these vectors to deliver the Herpes Simplex thymidine kinase gene to tumor cells will be evaluated in dogs with spontaneously occurring lymphoma. Dogs will be monitored to determine the impact of therapy on disease course and duration. The CD40 targeting methodology will provide enhanced imaging and diagnostic capabilities in addition to gene delivery and therapy. The technology and knowledge derived from these experiments will provide the most rigorous evaluation of this approach possible prior to human clinical trials. Ultimately, the use of the canine model and the vectors chosen will allow rapid translation of our findings into human clinical trials. Finally, this work promises to have the additional benefit of developing associated technologies that will not only assist in treatment, but may significantly improve diagnosis as well.